1. Field of the Invention
The present invention relates to equipment for separating molten sulfur from associated gases in industrial operations producing molten sulfur, such as oil refineries. More specifically, this invention relates to a seal for a sulfur trap.
2. Description of the Related Art
Gaseous compounds containing sulfur, such as hydrogen sulfide, mercaptans, carbonyl sulfide, carbon disulfide, exist in natural gas. Such gaseous compounds are produced as by-products in petroleum refining operations.
In industrial applications, gas streams containing sulfur compounds are processed to remove sulfur (primarily in the form of hydrogen sulfide). The gas streams are then further processed to form liquid sulfur in sulfur recovery units.
Conventional sulfur recovery units include a seal leg or trapping device to separate molten sulfur from the gas stream. The molten sulfur is condensed from the remaining gas stream.
The discharge into the atmosphere of residual tail gases associated with such molten sulfur, such as sulfur dioxide and hydrogen sulfide, is environmentally unacceptable. It is therefore necessary to separate the elemental sulfur from the tail gases associated therewith.
Sulfur traps associated with sulfur recovery units, as historically designed, include two concentrically arranged vertical pipes. The vertical pipes may extend approximately twenty feet to twenty-five feet into the ground. The outer pipe is capped at its lower end. The inner pipe lower end is displaced above the capped lower end of the outer pipe allowing molten sulfur to flow from the inner pipe to the annular space between the pipes. Molten sulfur is received into the inner pipe, flows downwardly from the inner pipe and upwardly in the annular space between the inner pipe and the outer pipe to a discharge pipe connected to the outer pipe. The discharge pipe transmits the sulfur into a sulfur storage tank where the sulfur may be maintained until pumped out for shipping or other disposition. A jacket is provided outside the outer pipe, with steam circulated between the jacket and the outer pipe to maintain the temperature of the sulfur trap above 250 degrees Fahrenheit and accordingly to maintain the sulfur in a liquid phase. The annular arrangement of the inner pipe and outer pipe provides a liquid trap preventing tail gases from being transferred in the storage tank.
Kuvasnikoff et al U.S. Pat. No. 4,185,140, Sims U.S. Pat. No. 4,255,408 and Singleton et al. U.S. Pat. No. 4,085,199 disclose processes for removing sulfur and sulfur compounds from sulfur bearing gases.
Stothers U.S. Pat. No. 4,504,459 discloses process and apparatus for extraction of elemental sulfur from sulfur compound gases.
Mori et al. U.S. Pat. No. 4,341,753 and Hellmer et al. U.S. Pat. No. 4,117,100 disclose processes and apparatus for converting sulfur dioxide and gas to sulfur.
Scott et al. U.S. Pat. No. 4,035,158 discloses a process and apparatus for burning hydrogen sulfide and other combustible fluids to recover sulfur.
Conventional in-ground sulfur traps require ground excavation and buried lines to install the concentric piping, the steam jacket and steam lines. In operation, the inner pipe or the annulus may become blocked or partially blocked from time to time by materials such as contaminated sulfur, carbon, catalyst dust, etc. To remove the blockage it is often necessary that the trap be partially disassembled and the inner pipe or annulus rodded out to restore circulation.
Operating pressures upstream of the conventional in-ground sulfur traps must be limited due to the nature of the liquid trap. Other disadvantages of conventional sulfur seal systems are that they extend 20′ or more into the earth, and that they are not easily cleaned.
U.S. Pat. No. 5,498,270 by this inventor discloses a sulfur trap that includes a sphere that engages an upwardly extending cylinder in a first position and that floats in the molten sulfur contained in the upper chamber in a second position.
The sulfur trap disclosed in U.S. Pat. 5,498,270 provided improved sealing over the prior art sulfur separation systems while allowing the process to operate at relatively high pressures upstream of the seal. Additionally, it did not require deep excavation and was relatively easy to clean.
The present invention comprises an improvement to the art by providing a self-cleaning mechanism on the trap enhancing the sealing interface.